It is known, for the grinding of cement clinker, cement raw material, coal and similar grinding stock, to use grinding bodies which have a hollow form. The hollow form of the grinding bodies affords the advantage of a considerable weight saving, as compared with solid grinding bodies. One disadvantage is that, where hollow bodies are concerned, because of the limited thickness of the shell, wear is a more serious problem than in the case of solid grinding bodies. So that unnecessarily high wear does not occur, the grinding bodies therefore have to be produced in such a way that they have as low a wear as possible. A production method, known from prior public use, for such hollow grinding bodies is composite casting. For casting, a casting mold is used which has an inner cavity in which a casting core is arranged in such a way that an interspace remains. Casting material is poured into this interspace, so that a shell-like body is obtained after solidification. There is, then, in this case, the difficulty that the casting core has to be fixed in the inner cavity of the casting mold. Furthermore, gases emerging from the casting core have to be discharged. It is known, for this purpose, to hold the core by means of a core supporting structure consisting of steel tubes. The steel tubes are of hollow form, so that gases can be discharged from the core through them. In order to prevent undesirable interactions between the core supporting structure and the casting material, the following methods for protecting the core supporting structure are known from prior public use:
In a first method, the core supporting structure is encased with ceramic material. So that the core supporting structure can be removed from the grinding body after the solidification of the casting material, a plurality of holes are made in the shell of the grinding body. The core supporting structure, together with its ceramic casing, is removed through these. The holes which have thus occurred have a relatively large diameter. During grinding, the edges of these holes obstruct the rolling of the grinding body. What may be referred to as edge bearing occurs. This leads to increased loads on the grinding body, so that it is subjected to increased wear at these points. Particularly where grinding bodies consisting of brittle material are concerned, chipping easily occurs in this region and ultimately may lead to a failure of the grinding body.
In a second method, the tubes of the-core supporting structure are not encased ceramically in the region of the interspace, but, instead, remain unprotected. During the casting operation, they are exposed directly to the casting material. The result of this is that, during the casting operation, there is, at least partially, a fusion of the casting material with the surface of the tubes of the core supporting structure. The core supporting structure is therefore not removed after the solidification of the casting material. It remains in the grinding body. Although edge bearing then also arises during operation, there is no longer any chipping in this region because the core tubes are fused in the same way as in composite casting. The disadvantage of this method is that, on account of the fused-in core tubes the core supporting structure can no longer be removed and is lost.